Hydrocarbon lubricating oil containing a polymer of a conjugated diolefin as a viscosity index improver



Unitcd States ate 3,547,821 HYDROCARBON LUBRICATING (BIL CUNTAIN- ING A POLYMER OF A QONJUGATED UKULE- FIN AS A VISCOSITY INDEX IMPRUVER Frederic C. McCoy, Beacon, and Edwin C. Knowles, Poughkeepsie, N.Y., assignors to Texaco Inc, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 13, 1967, Ser. No. 682,579 Int. Cl. (310m 1/46 U.S. Cl. 252-49.8 8 Claims ABSTRACT OF THE DHSCLOSURE Lubricating oil composition having an improved viscosity index containing a polymer of a conjugated diolefin in the cis-1,4 form having a molecular weight ranging from about 75,000 to 2,000,000, and a lubricating oil composition of improved viscosity index having high thermal stability containing a hydrocarbyl phosphite.

This invention relates to a novel mineral lubricating oil composition having an improved viscosity index containing a polymer of a conjugated diolefin in the cis-l,4 form having a molecular weight in the range of 75,000 to 2,000,000. This invention also relates to such an improved lubricating oil composition having an enhanced level of thermal stability containing a hydrocarbyl phosphite.

Lubricating oil compositions for internal combustion engines must function under a wide range of temperatures including a cold start-up period, a warm-up period, and a relatively high engine operating temperature. A high proportion of todays automobiles are used discontinuously as on short shopping trips with the result that the lubricating oil composition is constantly being heated and cooled over the broad range of temperatures. A motor oil composition must be sufficiently fluid at low or cold starting temperatures to permit easy starting and must also have suflicient viscosity at high engine temperatures to provide effective lubrication under these conditions. In addition to these requirements, there is a trend in the U.S. today to produce a single multi-viscosity motor oil which can provide the required lubrication in any season of the year ranging from the very cold northern winters to the hot southern summers.

Since the viscosity index of many straight mineral oils is relatively low, i.e., the viscosity changes to such an extent with changes in temperature that the oils are not suitable as motor oils, it is conventional to add a viscosity index modifier to a refined mineral lubricating oil to produce a motor oil composition which will provide effective lubrication at both low and high temperatures. Many types of additives have been employed for this purpose including polybutenes, ethylene-propylene copolymers, polymethacrylates and polymers of unsaturated organic compounds, such as aliphatic esters of unsaturated monocarboxylic or polycarboxylic acids. The conventional viscosity index modifiers are not entirely satisfactory, however. A widely used commercial viscosity index modifier is believed to be responsible for the buildup of undesirable deposits on the intake valves and ports of spark-ignited internal combustion engines with very detrimental elfects on the engine. Also, the trend toward all-season multi-viscosity motor oil compositions requires an inordinately high proportion of a conventional viscosity index modifier in the oil which is expensive and may reduce the lubricating properties of the oil.

It has also been found that the service life of a viscosity index modifier is adversely affected by todays high speed engines. In the presence of the severe shear- 3,547,821 Patented Dec. 15, 1970 ing action of the engine and at high engine temperatures the viscosity index modifier tends to gradually lose its elfectiveness for controlling the viscosity of the lubricating oil thereby seriously shortening the useful life of the motor oil.

A novel lubricating oil composition of high viscosity index has now been discovered containing a relatively small amount of a viscosity index modifier. There has also been discovered a lubricating oil composition of high viscosity index having an enhanced level of thermal stability.

In accordance with this invention, there is provided a mineral lubricating oil composition of high viscosity index containing from about 0.1 to 5 percent by weight of an effective viscosity-increasing amount of a stereo regulated polymer of a conjugated diolefin of from 4 to 5 carbon atoms having a number average molecular weight in the range from 75,000 to 2,000,000 in which a substantial proportion of the polymer is in the cis-1,4 form. There is also provided a lubricating oil composition of high viscosity index and of enhanced thermal stability containing from about 0.05 to about 2.0 weight percent of a hydrocarbyl phosphite represented by the formula (RO) P in which R is a monovalent hydrocarbon radical having from 1 to 18 carbon atoms.

The viscosity index modifier of this invention comprises polymers of C and C conjugated diolefins having number average molecular weight ranging from about 75,000 to 2,000,000 and in which a substantial proportion of the polymers are in the cis-l,4 configuration. As a minimum, the viscosity index modifier should contain about 35 percent by weight of the diolefin polymer in the cis-l,4 form. It is desirable that the amount of the cis-l,4 polymer in the total polymer should be as high as practicable, generally from to 100 percent and preferably at least of the total viscosity index modifier. In general, the viscosity index modifier will have a number average molecular weight ranging from about 75,000 to about 2,000,000 with a preferred molecular weight range being from about 75,000 to 300,000.

The viscosity index modifier of the invention is formed from a conjugated diolefin having from 4 to 5 carbon atoms. Specific diolefins which can be employed are butadiene, isoprene and 1,3-pentadiene. These diolefins may be employed alone or in combination as copolymers to produce the viscosity index modifier.

Methods for polymerizing conjugated diolefins to polymers of the cis-l,4 form are well known. The conjugated diolefin or mixture of corrugated diolefins are polymerized at temperatures ranging from about 0 to about C. in the presence of a catalyst, such as metallic lithium, lithium alkyls, such as ethyl lithium, n-butyl lithium, hexyl lithium, lithium dihydrocarbon amide, and complexes, such as titanium tetrachloride with aluminum trialkyls. Emulsion polymerization using free radical catalysts, such as alkali metal persulfates and organic hydroperoxides for example, is also a suitable method for preparing the diolefin polymers. How ever, the emulsion polymers are higher in their content of trans isomer and are thus somewhat less desirable for the purpose of this invention than those in which metal alkyls are used as catalysts.

The lubricating oil composition of the invention is prepared by blending a minor amount of the diolefin polymer into a lubricating oil base. In general, the lubricating oil base will be a mineral lubricating oil, parafiinic, naphthenic or mixed base oil, of lubricating viscosity. The lubricating base oils have viscosities ranging from about 75 to about 500 S.U.S. at 100 F. The solubility of the conjugated diolefin polymer in the mineral lubrieating oil base is greatly facilitated by first dissolving the polymers in a small amount of a solvent such as benzene, toluene or tetrahydrofuran, adding this mixture to the lubricating oil base and stripping off the solvent. Alternatively, a concentrate containing up to about l% by weight of the polymer in mineral oil may be prepared by the same technique, and the concentrate added to give the desired concentration of polymer in the finished motor oil. In general, the polymers are added to provide a concentration ranging from about 0.1 to about weight percent of the lubricating oil composition with the preferred concentration ranging from about 0.2 to 2 weight percent.

The thermal stability of the lubricating oil composition of the invention is substantially enhanced by adding a specific oxidation inhibitor, i.e., a hydrocarbyl phosphite defined above, to the lubricating oil composition. Efiective phosphites' include tri-2-ethylhexyl phosphite, triethyl phosphite, tricyclohexyl phosphite, triphenyl phosphite, trinonylphenyl phosphite and the like. Other inhibitors which are known to be effective when used in solid elastomers, both natural and synthetic were ineffective or harmful in the lubricating oil of the invention where the elastomer is in solution in mineral oil. In general, the hydrocarbyl phosphite is employed in a range from about 0.05 to 2.0 weight percent of the lubricating oil composition,

The following examples illustrate the practice of this invention.

EXAMPLE 1 Lubricating oil compositions were prepared from a mineral oil of lubricating viscosity containing a commercial polybutadiene viscosity index modifier. The viscosity index modifier, Additive A, was a cis-1,4 polymer of butadiene having a number average molecular weight of about 300,000 and consisting of about 90 percent of the cis-1,4 form. Toluene was employed as a solvent for the polymer which was then dissolved in the oil, and the toluene stripped out by heating in a stream of nitrogen. The viscosity, viscosity index and other properties of the base oil and of the additive-containing oils are shown in Table 1 below.

TABLE 1 Base oil plus Base oil plus 0.5% addi- 2% additivs Base oil tive A A Kin. vis. at 100 F. cs. 73. 9 103.4 203. 7 Kin. vis. at 210 F. cs. 8. 44 12. 35 40. 5 Vise. Index 91. 5 107 134 Your Point, F +10 +5 +5 EXAMPLE 2 The base oil in this example was a refined mineral lubricating oil having the following properties:

Gravity, API 31.9 Vis. kin. at 100 F. 31.8 Vis, kin. at 210 F. 5.23 Viscosity index 104 Pour point, F 0

The base oil was blended with a viscosity index modifier to form a lubricating oil containing 0.6 weight percent of a cis-1,4 polybutadiene having an average number molecular weight of 280,000. The thermal stability of this oil and of a similar oil containing 0.2 weight percent of tri-(Z-ethylhexyl) phosphite as shown by the loss of kinematic viscosity at 100 F. was determined following treatment in an Oven Test for hours at 250 F. In this test, the oil is allowed to stand in a four ounce bottle stoppered with glass wool. Kinematic viscosity at F. is measured at the beginning and end of the test.

The oil containing the viscosity index modifier but no phosphite suffered a loss of 21.4 percent in kinematic viscosity at 100 F. following the Oven Test. In contrast, the oil also containing the tri(2-ethylhexyl) phosphite had a loss of 3.5 percent in kinematic viscosity at 100 F. following the Oven test. The thermal stability of the oil with the phosphite additive was 82.5 percent better than that of the polymer-containing high viscosity index oil.

EXAMPLE 3 The base oil in this example was a compounded mineral lubricating oil consisting of 92.1 weight percent refined parafiinc oil, 6.9 percent conventional detergent-dispersant-wear inhibiting additives, 0.5 percent of a commercial pour point depressant and 0.5 percent cis-1,4 polybutadiene of 400,000-450,000 number average molecular weight, the compounded oil having a kinematic viscosity of 53.8 cs. at 100 F.

This base oil had a 20 percent loss of kinematic viscosity at 100 F. after undergoing the Oven Test described in Example 2 above.

Adding 0.2 weight percent of tri-(2-ethylhexyl) phosphite to the above oil improved the thermal stability of the oil by 49 percent.

Adding 0.2 Weight percent of tri(nonylpheny1) phosphite to the base oil improved its thermal stability by 30 percent.

Other oxidation inhibitors, such as 2,6-ditertiary butyl p-cresol, tertiary butyl hydroquinone, methylene bis- (hindered phenol) and 2(N,Ndi(sec.butyl p-phenylene diamine) which are known in the art as oxidation inhibitors for solid elastomers were ineifective for improving the thermal stability of the oil containing dissolved polybutadiene, In fact, most of these additions produced a substantial degradation in the thermal stability of the oil containing dissolved polybutadiene.

Novel lubricating oil compositions of high viscosity index based on a relatively small amount of a viscosity index modifier as well as lubricating oils of enhanced thermal stability have been described and shown to be highly effective. Obviously, many modifications of the invention may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A lubricating oil composition comprising a major proportion of a hydrocarbon lubricating oil and a viscosity index improving amount of a polymer of a conjugated diolefin of from 4 to 5 carbon atoms, said polymer having a number average molecular weight in the range from about 75,000 to 2,000,000 and having a substantial proportion of polymers in the cis-1,4 form, and from about 0.05 to 2.0 percent by weight of a hydrocarbyl phosphite having the formula (RO) P in which R is a hydrocarbyl radical having from 1 to 18 carbon atoms.

2. A lubricating oil composition according to claim 1 in which R is an alkyl radical.

3. A lubricating oil composition according to claim 1 in which R is a phenyl radical.

4-. A lubricating oil composition according to claim 1 inh which said alkyl phosphite is tri(2-ethylhexyl) phosp ite.

5. A lubricating oil composition according to claim 1 in which said phosphite is tri(nonylphenyl) phosphite.

6. A lubricating oil composition according to claim 1 in which said polymer has a number average molecular 5 weight in the range from about 75,000 to 2,000,000 and 3,244,650 having at least 35 percent in the cis-1,4 form. 3,296,134 7. A lubricating oil composition according to claim 1 3,312,621 in which said polymer is a polymer of butadiene. 3,329,613

8. A lubricating oil composition according to claim 1 5 in which said polymer consists of at least 90 percent of the cis-1,4 form.

References Cited UNITED STATES PATENTS 2,304,874 12/ 1942 Barnard 25249.8

3,056,823 10/1962 Heckenbleikner et a1.

3,115,465 12/1963 Orlolf et al. 25249.8X

FOREIGN PATENTS France.

DANIEL E. WYMAN, Primary Examiner 10 W. H. CANNON, Assistant Examiner US. Cl. X.R.. 

